1. Field of the Invention
The present invention relates to a diesel engine with a precombustion chamber.
2. Description of the Related Art
In a known diesel engine equipped with a precombustion chamber, the precombustion chamber is normally arranged above and slightly offset from the end portion of the main combustion chamber, i.e., is positioned in a direction perpendicular to the longitudinal axis of the engine body (see, for example, Japanese Unexamined Utility Model Publication No. 62-152022).
Where, however, a pair of camshafts are used for driving an intake valve and an exhaust valve, if the precombustion chamber is arranged above and slightly offset from the end of the main combustion chamber, in the direction perpendicular to the longitudinal axis of the engine body as mentioned above, one of the camshafts is positioned close to the precombustion chamber and the other camshaft is remote from the precombustion chamber. In this case, since the temperature of the precombustion chamber becomes very high, if one of the camshafts is arranged close to the precombustion chamber and the other camshaft is remote from the precombustion chamber, the temperature of the camshaft close to the precombustion chamber, and the temperature of the bearing for the camshaft close to the precombustion chamber, become high due to a transfer of heat from the precombustion chamber. Accordingly, when the temperature of the camshaft and the temperature of the bearing of the camshaft become high, as mentioned above, the cams of the camshaft are thermally expanded, and thus the cam phases of the cams will become different from the required cam phases. As a result, a problem arises in that the opening and closing timing relationship between the intake valve or the exhaust valve driven by the camshaft close to the precombustion chamber and having a high temperature, and the intake valve or the exhaust valve driven by the camshaft remote from the precombustion chamber and having a relatively low temperature, will not meet the required opening and closing timing relationship. Further, as mentioned above, if the temperature of only one of the camshafts and the temperature of the bearing of that camshaft become high, that camshaft and the bearing thereof are subjected to considerable changes in temperature when the engine is repeatedly operated and stopped, and as a result, a problem arises in that the operating life of the overheated camshaft and bearing thereof will be shorter than that of the remote camshaft and bearing thereof.
Furthermore, in a direct injection type Diesel engine, the fuel injectors do not project from the cylinder head to a great extent, but in a Diesel engine equipped with a precombustion chamber, since the fuel injector is arranged above the precombustion chamber, the fuel injector is projected far from the cylinder head. In this case, where the precombustion chamber is arranged above and slightly offset from the end of the main combustion chamber, perpendicular to the longitudinal axis of the engine body as mentioned above, the fuel injector is laterally projected far from the cylinder head. If the fuel injector is laterally projected far from the cylinder head, there is a much greater chance that the fuel injector and the piping thereof will come into contact with other parts of the engine, and as a result, a problem arises in that the fuel injector and the piping thereof will be damaged.